Question

I’ve finally got around to starting windows phone dev. I’m not very good at it yet, but anyway, I hope you guys understand what I want to do here.

From what I’ve learnt from other programmers, an ObservableCollection can be updated in live time whilst it is databound to an object, such as a listbox. All changes to the ObservableCollection will cause the UI of the object it’s databound to update it’s items.

So what I’m trying to do, is download a file from my server, parse it with json, then update the ObservableCollection with the new data. However, the webclient doesn’t seem to be downloading the new data until the app is re opened!

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Here’s a gif showing how the app works at the moment:

And here’s my code (cut down a bit):

Dim aList As New ObservableCollection(Of classes.consoles)

Private Sub PhoneApplicationPage_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
        checkforconsoles()
End Sub

Public Sub checkforconsoles()
        Dim wc As New WebClient()
        AddHandler wc.DownloadStringCompleted, AddressOf downloaded
        wc.DownloadStringAsync(New Uri("http://localhost/api/?function=GetConsolesForUser&userid=" & id))
    End Sub

    Private Sub downloaded(sender As Object, e As DownloadStringCompletedEventArgs)

        aList.Clear()
        'MessageBox.Show(e.Result)

        Dim o As JObject = JObject.Parse(e.Result)

        Dim jarray As JArray = DirectCast(o("results"), JArray)

        Try
            Dim i As Integer = jarray.Count()

            For i = 0 To jarray.Count() - 1 Step 1

                Dim id As String = jarray(i)("id").ToString
                Dim name As String = jarray(i)("name").ToString
                Dim image As String = jarray(i)("image").ToString

                MessageBox.Show(name)

                Dim c As classes.consoles = New classes.consoles()
                c.categoryimage = New Uri(image)
                c.categoryname = name
                c.categoryid = id

                aList.Add(c)
            Next

            listBoxview.ItemsSource = aList
            StackPanel1.Visibility = Windows.Visibility.Collapsed
            StackPanel2.Visibility = Windows.Visibility.Visible

        Catch ex As Exception
            StackPanel2.Visibility = Windows.Visibility.Collapsed
            StackPanel1.Visibility = Windows.Visibility.Visible
        End Try

    End Sub

Private Sub ApplicationBarIconButton_Click_1(sender As System.Object, e As System.EventArgs)
    checkforconsoles()
End Sub

Does anybody have any clue what’s wrong? 🙁

Thanks in advance.

Answer 1

It’s a cachine issue with the WebClient. You can append a random query string to ensure that the URL is always unique so that the WebClient doesn’t cache the results. One way to do this is to add a random GUID value since it’s very unlikely to generate two of the same GUIDs in a short time frame.

wc.DownloadStringAsync(New Uri("http://localhost/api/?function=GetConsolesForUser&
                         userid=" & id & "&random=" + Guid.NewGuid().ToString()))